COPEPODA. 15RANCHIURA. 



437 



contains 

 paii- of 



A 



R 



The Branchiura are often placed near the Caliyidca, but they 

 differ from them and from the true Copepoda in several essential par- 

 ticulars. In the general body form they certainly resemble the 

 Calicjidw except in the abdomen, which is split into two plates 

 (caudal fins). Their internal structure, however, and the structure 

 of the appendages distinguish them from the above-mentioned 

 parasitic Crustacea. A large suctorial tube projects above the mouth, 

 and in it are concealed finely serrated mandibles and styliform 

 maxilla*. A little above this proboscis there is inserted a long 

 cylindrical tube, which terminates in a retractile styliform spine, and 

 the ducts of a 

 glandular tubes 

 said to be poison glands. 

 Powerful organs of attach- 

 ment are placed on each 

 side of and beneath the 

 mouth ; they consist of 

 two parts (1) of an an- 

 terior pair of appendages 

 which correspond to the 

 anterior maxillipeds and 

 are in Argulus modified 

 into large sucking discs, the 

 hook-bearing terminal por- 

 tion being reduced ; and (2) 

 of a posterior pair, which 

 corresponds to the second 

 pair of maxillipeds, and is 

 provided with numerous 

 spines on its broad basal 

 portion, a tactile protube- 

 rance and two curved termi- 

 nal claws at its extremity. 

 Next to these come the four paired swimming feet of the thoracic re- 

 gion, which, with the exception of the last, are, as a rule, covered by the 

 sides of the cephalo-thoracic shield. Each of these consists of a large 

 many-jointed basal portion, and two much narrower rami, which are 

 beset with long swimming seta* and in their form and setigerous 

 investment are not unlike the biramous appendages of the Cirripedia, 

 being like them derived from the Copepod-like feet of the larva 

 (fig- 347). 



Fn;. 347. Young male of Argnlus foliaceua. A', 

 Anterior antenna? ; Sg, sucker (anterior maxilli- 

 peil) ; Ef", maxillipeil ; Sf, swimming feet, 

 -??, rostrum ; St, spine ; D, intestine ; T, testes. 



